Electric motors are manufactured in a variety of types and configurations. Typically, a motor includes a stator, a rotor, a shaft, and bearings. These assembled parts create a motor assembly around which a motor housing is used to provide structure and support. Motor housings often require a high level of precision to tightly fit and contain the enclosed motor assembly. Current methods for creating motor housings are expensive. For example, the housing could be machined to the exact specifications of the motor housing. This method, however, requires high precision machining capabilities and involves an extremely low tolerance for error in the manufacturing process.
Alternately, motor housings are often created through a two step process. The first step involves creating a cylinder slightly smaller than the motor assembly's final diameter. The second step involves, a process of fine-sizing the motor housing. Several methods of fine-sizing are known in the art. The motor assembly is then inserted into the motor housing, after the housing has been fine-sized.
FIGS. 1A-1D show one method of fine-sizing a motor assembly. It involves drawing a solid metal block through a pre-sized cylindrical tube. In FIG. 1A, a motor housing 100 is shown as a cylindrical tube having a hollow interior. The hollow interior 105 in FIG. 1A, acts to enclose and protect a motor assembly (not shown).
First, a coarse-form cylindrical metal tube is created. Next, a secondary fine-sizing operation is performed. For example, either a cylindrical or spherical metal block 110 is drawn through the motor housing 100, to expand the housing 100 to the specified tolerances and thereby accommodate the motor assembly. FIG. 1A illustrates a cylindrical metal block 110 that is chosen with a circumference equal to or slightly greater than that of the motor assembly. Once the corresponding metal block 110 is chosen, it is drawn through the motor housing 100 along a co-axial line A-A in steps as shown in FIGS. 1A-1D. This same expansion process can be completed with a spherical metal form drawn through the motor housing.
FIG. 1B illustrates the first step in the fine-sizing process, wherein the leading edge 115 of the metal block 110, deforms the proximal end 120 of the motor housing 100. In some embodiments the metal block's leading edge 115 is beveled to ease the drawing process. FIG. 1C illustrates an intermediate stage of the drawing process. FIG. 1D illustrates the step wherein the metal block 110 has been completely drawn through the motor assembly 100. At this point, the size of the motor housing 100 corresponds to the diameter of the motor assembly.
This type of fine-sizing involves additional manufacturing machinery that leads to higher production costs and increased complexity associated with the housing manufacturing process. Fine-sizing also requires extremely accurate tolerances associated with matching the stator's outer diameter to the fine-sized tube's inner circumference. Furthermore, these expansion based fine-sizing methods make it impossible to easily correct an oversize error. Once the block is drawn through the pre-sized tube or the expansion device deforms the inner circumference of the tube, the pre-sized tube's circumference can only be further expanded. Accordingly, it is difficult to correct an accidental or erroneous over-expansion.